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Subject[PATCH] kvm: x86: disable shattered huge page recovery for PREEMPT_RT.
Date
If a huge page is recovered (and becomes no executable) while another
thread is executing it, the resulting contention on mmu_lock can cause
latency spikes. Disabling recovery for PREEMPT_RT kernels fixes this
issue.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/mmu.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index fd6012eef9c9..cf718fa23dff 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -51,7 +51,12 @@
extern bool itlb_multihit_kvm_mitigation;

static int __read_mostly nx_huge_pages = -1;
+#ifdef CONFIG_PREEMPT_RT
+/* Recovery can cause latency spikes, disable it for PREEMPT_RT. */
+static uint __read_mostly nx_huge_pages_recovery_ratio = 0;
+#else
static uint __read_mostly nx_huge_pages_recovery_ratio = 60;
+#endif

static int set_nx_huge_pages(const char *val, const struct kernel_param *kp);
static int set_nx_huge_pages_recovery_ratio(const char *val, const struct kernel_param *kp);
--
1.8.3.1
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